1. Field of the Invention
The invention relates to a method of manufacturing a pressure control valve, particularly to improvements in a process of assembling a diaphragm unit in the method of manufacturing the pressure control valve, and, for example, to the method of manufacturing the pressure control valve, which is effective for use in techniques of manufacturing a fuel pressure control valve for controlling a fuel supply flow rate in accordance with fuel pressure.
2. Related Art Statement
In general, in a vehicle such as a motor vehicle, there has been used a fuel pressure control valve provided with a diaphragm unit in a fuel supply path for delivering fuel in a fuel tank to an engine.
In the fuel pressure control valve as described above, a fuel introduction path and a fuel discharge path, which are communicated with a control valve chamber, are formed in a housing constituting the control valve chamber together with the diaphragm, and a valve body for controlling the flow of the fuel is mounted to the inlet side of the fuel discharge path in a manner to be interlocked with the diaphragm.
In the fuel pressure control valve as described above, heretofore, the diaphragm has been caulked and fixed, and thereafter, a return spring has been set on the diaphragm. Subsequently, a case is mounted to the housing in a manner to cover the diaphragm and a return spring, and a double caulking construction in which the case is caulked and fixed to the housing is adopted, as shown U.S. Pat. No. 4,936,342.
However, in this double caulking construction, a diaphragm holder as a part of the diaphragm unit is required, and also a special process for caulking the case to the housing is required, thereby disadvantageously lowering the workability.
Therefore, there has been proposed a single caulking construction in which the diaphragm and the return spring are caulked simultaneously. According to this single caulking construction, the diaphragm holder as the part of the diaphragm unit can be dispensed with, so that the special process for caulking the case to the housing can be dispensed with.
However, when the case is caulked to the housing, the diaphragm stays in a free state where the diaphragm is not positioned to the case and the housing, whereby a shift of position takes place between the diaphragm and the case, so that an end portion of the diaphragm is bitten into the case. As a result, fuel leakage may occur from the portion where the diaphragm is bitten into.
Then, as described in Japanese Patent Laid-Open No. 1-138368, such a manufacturing method is proposed that internal threads are formed on an armature (receiver); an externally threaded jig is inserted from the side of an atmospheric chamber of the case and threadably coupled to the internal threads of the armature; and the case is caulked to the housing in a state where this jig holds the diaphragm through the armature to position the diaphragm.
However, in the method in which the diaphragm is held by this jig and positioned, it is necessary to form the internal threads on the armature for supporting the diaphragm, and it is also necessary that the externally threaded jig is inserted through a pipe having negative pressure communicating with the atmospheric chamber of the case and the armature is positioned and held by use of this jig, so that such disadvantages are presented that not only the work is troublesome but also the positioning accuracy between the diaphragm and the case is lowered. Furthermore, a hole for receiving the jig is required at the top end of the case.